1. Field of the Invention
The present invention relates generally to inhalation devices. More particularly, the invention concerns an improved aerosol inhalation apparatus for medicinal use that delivers a mist of properly sized aerosol particles of medicament to the patient with a very high-level of efficiency.
2. Discussion of the Prior Art
Therapeutic aerosols are commonly administered to patients suffering from numerous types of pulmonary diseases. Specific medications include beta.sub.2 agonizes, anticholinergies, cromolyn sodium, and steroids. More recently the aerosol method of delivery has been used to administer Pentamidine to patients afflicted with AIDS, Tobramycin for cystic fibrosis, Morphine for pain, and is presently under consideration as a delivery means for use in drug delivery using gene therapy. Experience has shown that the use of aerosols to treat lung disease is highly advantageous in that it produces optimal therapy with minimum side effects.
Both physical and clinical factors affect aerosol deposition in the lungs. Physical factors include inertial impaction, sedimentation, and diffusion. Clinical factors include particle size, ventilatory pattern and lung function. Aerosols larger than 5 micron mass median aerodynamic diameter (MMAD) poorly penetrate the upper respiratory tract. Those in the 1 to 2 micron range tend to have their maximum deposition in the lung parenchyma.
In general the devices used for producing medical aerosols fall into two categories; the small volume nebulizer (SVN), and the metered dose inhaler (MDI). The small volume nebulizer (SVN) has traditionally been the apparatus of choice for delivery of therapeutic aerosols. The delivery apparatus typically consists of a disposable or reusable nebulizer, a mouthpiece or facemask, and a pressurized gas source usually oxygen or air. The metered dose inhaler (MDI), on the other hand, typically contains the active drug, a metering valve, and chlorofluorcarbon (CFC) or hydrofluoroalkanes (HFA) propellants. The drug-containing canister of the device is generally fitted to a mouthpiece actuator and activation by compression of the canister into the mouthpiece results in the release of a unit dose of medication.
As stated in current literature (Respiratory Care, Vol. 38, No. 38, August 93, and Advance for Respiratory Care Practitioners, Aug. 9, 1993, pages 8-10) the most limiting factor in the use of aerosolized medication is the inefficient mist production by current commercial nebulizer systems, whether they are of the small volume nebulizer (SVN) or metered dose inhaler (MDI) variety. Research has shown that most state-of-the-art commercial units deliver less than 10% of the original dose of medication to the patient's respiratory tract. (Respiratory Care, Vol. 38, #8, August 1993, Page 877, and AARC Times, June 1993, Page 48.) The apparatus of the present invention provides a very substantial improvement over all existing prior art aerosol devices by increasing the efficiency of delivery of medication to the patient by a factor of 2 to 3 times that exhibited by currently available prior art nebulizer devices. As a further substantial benefit, the apparatus of the present invention functions in a manner to assure that the medicament particles delivered to the patient will be of optimum size for drug delivery to any or all areas of the lung where it can most effectively be utilized.
A highly successful general purpose aerosol inhalation apparatus for use in respiratory therapy procedures in the field of medicine is disclosed in U.S. Pat. No. 5,727,542 issued to the present inventor. The apparatus described in this patent converts liquid medication into an aerosol mist and provides for delivery of this mist with such high efficiency that up to 40% of the original dose of medication placed in the nebulizer can be delivered to the patient's lungs. The present invention comprises an improvement to the apparatus disclosed in U.S. Pat. No. 5,727,542 and provides for delivery of the aerosol mist to the patient at substantially equal efficiency. The present invention can also deliver drugs at these high efficiencies to patients on ventilators, where the device disclosed in U.S. Pat. No. 5,727,542 cannot.